The electronic properties of graphene, a two-dimensional crystal of carbon atoms, are exceptionally novel. For instance, the low-energy quasiparticles in graphene behave as massless chiral Dirac fermions which has led to the experimental observation of many interesting effects similar to those predicted in the relativistic regime. Graphene also has immense potential to be a key ingredient of new devices, such as single molecule gas sensors, ballistic transistors and spintronic devices. Bilayer graphene, which consists of two stacked monolayers and where the quasiparticles are massive chiral fermions, has a quadratic low-energy band structure which generates very different scattering properties from those of the monolayer. It also presents the unique property that a tunable band gap can be opened and controlled easily by a top gate. These properties have made bilayer graphene a subject of intense interest. In this review, we provide an in-depth description of the physics of monolayer and bilayer graphene f...

Properties of graphene: a theoretical perspective

Graphene-based hybrid nanostructures have attracted increasing interest worldwide. Benefiting from their remarkable electrochemical catalytic properties derived from chemical compositions and synergetic effects of multi-functionalities, these graphene-based hybrid nanomaterials will play a significant role in cutting-edge innovation for novel electrocatalysts. In this review, we summarize recent progress in the design and synthesis of graphene-based hybrid nanomaterials with controlled shape, size, composition and structure, and their application as efficient electrocatalysts for energy related systems. We conclude this article with some future trends and prospects which are highlighted for further investigations on graphene-based nanomaterials as advanced electrocatalysts.

https://pubs.rsc.org/en/content/articlepdf/2014/MH/C4MH00040D

Recent progress on graphene-based hybrid electrocatalysts

The pathway towards the realization of optical solid-state lasers was gradual and slow. After Einstein's paper on absorption and stimulated emission of light in 1917 it took until 1960 for the first solid state laser device to see the light. Not much later, the first semiconductor laser was demonstrated and lasing in the near UV spectral range from ZnO was reported as early as 1966. The research on the optical properties of ZnO showed a remarkable revival since 1995 with the demonstration of room temperature lasing, which was further enhanced by the first report of lasing by a single nanowire in 2001. Since then, the research focussed increasingly on one-dimensional nanowires of ZnO. We start this review with a brief description of the opto-electronic properties of ZnO that are related to the wurtzite crystal structure. How these properties are modified by the nanowire geometry is discussed in the subsequent sections, in which we present the confined photon and/or polariton modes and how these can be investigated experimentally. Next, we review experimental studies of laser emission from single ZnO nanowires under different experimental conditions. We emphasize the special features resulting from the sub-wavelength dimensions by presenting our results on single ZnO nanowires lying on a substrate. At present, the mechanism of lasing in ZnO (nanowires) is the subject of a strong debate that is considered at the end of this review.

ZnO nanowire lasers

Carbon and non-carbon support materials for platinum-based catalysts in fuel cells

A Review of the Design of Advanced Binders for High-Performance Batteries

Graphene as catalyst support: The influences of carbon additives and catalyst preparation methods on the performance of PEM fuel cells

Besides its interesting physical properties, graphene as a two-dimensional lattice of carbon atoms promises to realize devices with exceptional electronic properties, where freely suspended graphene without contact to any substrate is the ultimate, truly two-dimensional system. The practical realization of nano-devices from suspended graphene, however, relies heavily on finding a structuring method which is minimally invasive. Here, we report on the first electron beam-induced nano-etching of suspended graphene and demonstrate high-resolution etching down to ~7 nm for line-cuts into the monolayer graphene. We investigate the structural quality of the etched graphene layer using two-dimensional (2D) Raman maps and demonstrate its high electronic quality in a nano-device: A 25 nm-wide suspended graphene nanoribbon (GNR) that shows a transport gap with a corresponding energy of ~60 meV. This is an important step towards fast and reliable patterning of suspended graphene for future ballistic transport, nano-electronic and nano-mechanical devices.

/pdf/electron-beam-induced-nano-etching-of-suspended-graphene-1sb6s75bwx.pdf

Electron-beam induced nano-etching of suspended graphene

The time-resolved photoluminescence (PL) characteristics of single CdSe/ZnS nanoparticles, embedded in a poly(methyl methacrylate) layer, is studied at room temperature. We observe a strong spectral jitter of up to 55 meV, which is correlated with a change in the observed linewidth. We evaluate this correlation effect using a simple model, based on the quantum confined Stark effect induced by a diffusing charge in the vicinity of the nanoparticle. This allows us to derive a mean distance between the center of the particle and the diffusing charge of approximately 5 nm on average, as well as a mean charge carrier displacement within the integration time. These results are reproducible, even for particles which exhibit strong blueing, with shifts of up to 150 meV. Both the statistics and its independence of core-shell alterations lead us to conclude that the charge causing the spectral jitter is situated in the ligands or on its surface.

Role of the ligand layer for photoluminescence spectral diffusion of CdSe/ZnS nanoparticles

Quantum wells are created from ultrathin single-crystalline EuO layers to study the evolution of the optical band gap down to the single nanometer regime. We find that the EuO band gap is indirect—independent of quantum well thickness—and increases from 1.19 eV for bulk-like (d = 32 nm) to ≈1.4 eV in the ultrathin films (d = 1.1 nm). The observed band-gap widening is a clear sign of a quantum confinement effect, which can be used to control and modify the band gap in EuO-based all-oxide heterostructures.

Quantum confinement in EuO heterostructures

We investigate the whispering gallery modes (WGMs) of self-assembled single microspheres. They consist of a recently developed highly fluorescent π-conjugated copolymer and exhibit excellent optical properties with Q-factors up to 104. Under continuous laser irradiation, we observe a splitting of the highly degenerate spherical WGMs into a multiplet of lines. Comparison with the calculated spectral response of a weakly distorted sphere shows that the optical excitation induces a change of the optical path length in the microcavity so that it resembles a prolate spheroid. The separation of the lines is given by the ellipticity and the azimuthal mode number. Measurements in various gaseous environments suggest that the distortion is caused by light induced oxidation of the polymer. Our findings show that photooxidation can be a beneficial mechanism for in-situ tuning of optically active polymer structures.

/pdf/optically-induced-mode-splitting-in-self-assembled-high-66id1civa1.pdf

Günther M. Prinz

Papers

Graphene as catalyst support: The influences of carbon additives and catalyst preparation methods on the performance of PEM fuel cells

Electron-beam induced nano-etching of suspended graphene

Role of the ligand layer for photoluminescence spectral diffusion of CdSe/ZnS nanoparticles

Quantum confinement in EuO heterostructures

Optically induced mode splitting in self-assembled, high quality-factor conjugated polymer microcavities